Lamellar decanting module and block comprising plates that can be vertical

ABSTRACT

The invention relates to a lamellar decanting module comprising two interconnected plates, at least one of said plates being corrugated in such a way that the dips and peaks are inclined in relation to a first edge of said plate according to a non-zero degree angle and define inclined decanting tubes with the other plate. Said module is characterised in that the two plates ( 2, 3 ) have the same corrugated profile and are interconnected in connection regions defining a plane of symmetry (P) for the tubes ( 4 ) defined by said plates. A plurality of modules can be assembled in such a way as to form a block in which the plates are parallel to one of the faces.

I—TECHNICAL FIELD

The invention relates to a system of slats for separating bysedimentation solid particles in suspension in liquids such aseffluents, in particular a system well adapted to the clarification ofwaste waters, rendering surface waters drinkable and the production ofindustrial process effluents.

II—TERMINOLOGY

Diverse concepts will be used hereinafter with the following meanings:

Sedimentation plate or slat=plane or corrugated surface installed in atank called a lamellar sedimentation tank to recover particles detachedfrom the main fluid,

Sedimentation tube=conduit of essentially polygonal shape, generallyformed by the juxtaposition of two plates at least one of which iscorrugated, and disposed at a certain angle relative to the horizontalplane to effect the liquid-solid separation,

Module=group of two plates disposed to constitute sedimentation tubes,

Block=group comprising a plurality of assembled modules to facilitateuse,

Transition area=first portion of the sedimentation tube in which thetransition between turbulent flow and laminar flow occurs,

Useful length=portion of the sedimentation tube situated downstream ofthe transition area, in which phase separation occurs because of laminarflow conditions.

III—PRIOR ART

Existing lamellar sedimentation tank employ one of the following threeflow principles:

counter-current: the particles move downwards while the liquid beingtreated moves upward,

cross-current: the liquid moves horizontally while the particles movedownward,

co-current: the liquid and the separated particles flow in the samedirection, generally downward.

The invention is aimed particularly at the first category, namelycounter-current sedimentation, which is that most widely used inindustry.

Most existing systems (often referred to as of the “honeycomb” type) arebased on the use of separator tubes, which are usually polygonal,oriented at an angle from 45° to 65° to the horizontal plane.

In practice, the plates used have a waffle pattern, usually oftrapezoidal shape, disposed parallel to the vertical edge of the plates,and the inclination of the tubes formed in this way is determined by theangle at which the plates are mounted relative to the horizontal plane,i.e. an angle from 45° to 65°.

Inside the tubes, which are of hexagonal shape when the waffle patternis trapezoidal, the sludge flows over the inclined plane formed by thelower side of the hexagon (and thus a shorter side of the trapezoidalshape), at a speed that is slowed by friction resulting from the largearea of contact between the sludge and the slats because of thistrapezoidal section.

Moreover, the plates disposed this way run the risk of buckling and ofplastic deformation if the weight of the deposit becomes excessive,which in practice necessitates the presence of specific stiffeningarrangements or an increased thickness of the plate.

Thus prior art lamellar sedimentation tanks consist in practice of astack of parallel plates (in the lengthwise direction of the tank)offset relative to each other to take account of their inclination andforming a long assembly necessitating handling, relative positioning andstacking of a large number of inclined plates. Assembling the platesinto modules and the modules into blocks facilitates the use of theseplates by virtue of a portion of the assembly operations being carriedout outside the tank; however, there are still operations to be carriedout in the tank, which significantly increases the cost and the durationof which is difficult to reduce.

Moreover the blocks, which have the shape of non-rectangularparallelograms with inclined lateral faces consisting of the front andrear plates, are difficult to handle and ill-adapted to equippingstructures of non-rectangular shape.

Another type of commercially available lamellar block is ofparallelepipedal shape, consisting of vertical plates carrying wafflepatterns inclined relative to the sides of the plates; blocks of thiskind are routinely used as an orderly lining to increase the area ofcontact in gas-liquid and liquid-liquid contact devices. However, inthis type of use, the successive plates are disposed so that the wafflepatterns are crossed, to enhance the effect of mixing by crossing of theflows, with the result that there are not really any tubes.

A variant is disclosed in the document U.S. Pat. No. 5,384,178, whichdescribes a sedimentation assembly formed of modules of two verticalplates conjointly forming inclined tubes. To be more precise, eachmodule is formed by assembling two plates with different geometries, thefirst of which is corrugated and the other substantially plane, so thatthe tubes have trapezoidal, almost triangular, sections. To be moreprecise, the second plate has concave grooves that cap the crests of theother plates, which enables good relative positioning, but implies thatthe second plate penetrates into the concave portions of thecorrugations of the first plate. These modules can be stacked, thusforming an array of substantially triangular tubes. However, becausethese plates have corrugations in the same direction but of differentamplitudes, the tubes obtained by stacking two modules are smaller thanthose formed within each of the modules. The corrugations are notrectilinear in the sense that, at their ends, the tubes are bent untilthey are vertical and moreover because the walls of the tubes havecorrugations along their longitudinal axis. As a result of this, thesystem implies plates with at least two different geometries, each ofwhich is complex, and tubes that have different and varying sections.This leads to disadvantages not only in fabrication (time and costlinked to the necessity of providing two types of fabrication), but alsofor maintenance (in particular for cleaning corrugated, bent andnon-identical tubes).

Note also that this configuration with globally triangular tubes is morecompact, and therefore heavier than that of prior art blocks withhexagonal tubes.

A common drawback of the various existing systems is that in practicethey necessitate draining of the structures to install the blocks and toremove them.

IV—TECHNICAL PROBLEM AND SOLUTION OF THE INVENTION

An object of the invention is to alleviate the drawbacks cited above byproposing a module (of two plates) and a lamellar sedimentation system(with at least one block of plates) that combine at least some of thefollowing advantages:

sedimentation in tubes rather than between spaced plates, to improve theefficacy of sedimentation,

use of a tube shape minimizing the area of the slats in contact with theflow of sludge, to diminish sludge-slat friction, increase the rate offlow of the sludge, minimize the section necessary for allowing freeflow of sludge, and thereby increasing the available section for theflow of water,

vertical disposition of the modules the corrugations whereof areinclined to improve their mechanical strength and/or to reduce thethickness of the plates,

minimizing the number of different components to be provided,

minimizing the number of plates to be assembled to constitute a moduleof given width but of great length,

reducing the costs of use.

To this end the invention proposes, firstly, a lamellar sedimentationmodule including two plates fixed together, at least one of these plateshaving corrugations the crests and the troughs whereof are inclined to afirst edge of this plate at a non-zero angle and delimit with the otherplate inclined sedimentation tubes, characterized in that the two plateshave the same corrugated profile and are fixed together in connectingareas defining a plane of symmetry for the tubes defined by theseplates.

The identical corrugated profiles of the two plates enable them to beproduced by the same fabrication process and their symmetrical assemblyproduces tubes in a particularly simple way.

The crests and the troughs are preferably of trapezoidal shape, so thatthe sedimentation tubes have a hexagonal shape, which corresponds to astructure that is both robust and not very compact.

To facilitate the positioning of the plates at the time of assemblingthe module, the plates are advantageously symmetrical to each otheroverall (and therefore identical), so that superposition of the edges ofthe plates, ignoring a rotation, guarantees the correct positioning ofthe troughs (or the crests).

For obvious reasons of simplicity of fabrication and handling, theseplates are preferably rectangular in shape.

Likewise, for similar reasons of simplicity, the tubes are preferablyrectilinear, without bends at their ends.

The inclination of the tubes relative to said first edge isadvantageously in the range 45°-65°, preferably 55°-60°, which appearsto lead to very good sedimentation performance when the plates aredisposed vertically in the effluents to be treated, with the first edgedisposed horizontally.

The invention further proposes a lamellar sedimentation system includingat least one block formed of a plurality of plates, at least one pair ofwhich constitutes a module of the type defined hereinabove, whichimparts high stiffness to it.

A block of the above kind may include an odd number of plates butadvantageously includes a plurality of modules of which at least two aremodules assembled so that the modules conjointly delimit other tubes,the modules being fixed to each other in areas defining a plane ofsymmetry for those other tubes.

The other tubes advantageously have the same section as the tubes of themodules, in which case the block constitutes an array of identicaltubes, which therefore has substantially homogeneous performance at allpoints in the block.

For obvious reasons of simplicity of fabrication, the modules areadvantageously identical, which means in particular that a block has arectangular parallelepiped shape, the plates being perpendicular to oneof the faces of the block. The plates preferably extend perpendicularlyto the smallest dimension of the block, in other words the plates extendalong the largest two dimensions of the block, which encourages goodmechanical strength of the assembly. A rectangular parallelepipedgeneral shape of the above kind makes the block easy to manipulate andto accommodate in a sedimentation tank.

As already mentioned hereinabove, the block is advantageously disposedin the system so that the plates are vertical, with the first edgehorizontal; this means in particular that the block may be suspendedfrom a fixed portion of the system, with no risk of deformation of theblock by gravity.

Note that in this configuration sedimentation occurs along a locallytriangular portion (in a junction area between the two plates), whichencourages rapid evacuation of the sludge.

The blocks are constructed by grouping a certain number of modules andeach block may be provided with hooks or rings to facilitate handlingit. The modules may be assembled to constitute a block by clipping,adhesive bonding, heat welding or ultrasound welding.

The blocks may optionally be installed inside metal frames that can alsoserve for transportation and handling. The frame may advantageously bedemountable to enable easy replacement of the slats, according to therequirements of the treatment.

The disposition of the blocks in line with each other necessitatescompliance with the same orientation of the sedimentation tubes in orderto ensure that the end tubes of one of the blocks line up with thecorresponding tubes of the other block; this yields tubes in twosections that end up having the same length as the tubes entirelycontained within each block.

A modular structure is therefore obtained that adapts easily to theparticular disposition of the tank that is to contain the lamellarsedimentation system, which tank may be of any size and any shape,including circular. This enables the construction of large assemblies bydisposing the blocks in the treatment structures on supports providedfor this purpose or suspending them from existing structures, entirelyby mechanical handling means.

Where the block faces a tank wall to which the plates are perpendicular,the block is advantageously at a distance from that wall that leaves aspace between the slats and the walls to ensure the feeding and thedraining of the sedimentation tubes of the block that are incomplete.

The tubes preferably have a hydraulic diameter from 40 mm to 100 mmand/or the tubes preferably have a length from 15 to 30 times theirhydraulic diameter, which ensures good sedimentation performance.

Note that, compared to the blocks of the document U.S. Pat. No. 5,384178, the modules and blocks of the invention lead to a reduced weightfor a given volume without degrading the mechanical strength of theassembly, with tubes of larger section, and therefore with a lower riskof clogging, since there are no approximately plane plates betweenplates with large corrugations. The disposition of the invention enablesthe use, for a given sedimentation task, of an area of plates muchsmaller than that proposed by the document cited above, the plane plateshaving no function in sedimentation as such.

Unlike crossed orderly linings, the parallel disposition of thecorrugations (or waffle patterns) minimizes turbulence and prevents theformation of mixing roundabouts.

The present blocks significantly facilitate use and can even beinstalled in plant without emptying it or shutting it down.

V—DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

Objects, characteristics and advantages of the invention emerge from thefollowing description which is given by way of illustrative andnonlimiting example with reference to the appended drawings, in which:

FIG. 1 is a perspective view of a lamellar sedimentation module,

FIG. 2 shows a lamellar sedimentation block of the invention,

FIG. 3 is a partial top view of that block,

FIG. 4 is a detail view of a sedimentation tube in vertical section in aservice configuration,

FIG. 5 is a diagram of a block like that from FIGS. 2 and 3 fitted withattachment elements,

FIG. 6 is a top view showing a set of complete or incomplete blocksoccupying a predetermined rectangular space,

FIG. 7 is a diagram showing the cooperation of two blocks situated inline with each other in the FIG. 6 system,

FIG. 8 is a diagram of an installation including a sedimentation systemresting on supports,

FIG. 9 is a diagram of another installation including a sedimentationsystem integrated into a channel type activated sludge tank,

FIG. 10 is a diagram of another installation including a series ofsedimentation blocks disposed against a curved wall,

FIG. 11 is a view of that installation in vertical section, and

FIG. 12 is a diagram of a suspended installation.

FIG. 1 represents a sedimentation module of the invention.

The module 1 includes two plates 2 and 3 fixed together, for exampleadhesively bonded together.

These two plates include corrugations whose crests 2A or 3A and troughs2B or 3B are inclined relative to a first edge of the plates at anon-zero angle a; the troughs are fixed facing each other, and thecrests of the two plates delimit inclined sedimentation tubes 4.

The two plates have the same profile and are fixed in regions of theirtroughs that define an imaginary plane P that is a plane of symmetry ofthe tubes defined by the plates. Here the plates are identical in thesense that, in particular, their edges face each other; they aresymmetrical to each other with respect to the plane P. Their shape ispreferably rectangular, which is a particularly simple shape.

As shown in FIG. 2, a plurality of plates may be assembled to form ablock 10, here of globally rectangular parallelepiped shape, with anarray of identical hexagonal tubes. The FIG. 3 block may advantageouslybe analyzed as being formed of four modules 1 like that of FIG. 1, butthe number of modules per block can of course be different. The troughsof the plates form tubes 4′ which here are similar to those formed ineach module.

Here the troughs and the crests have the same profile so that the tubesconjointly formed by the crests of two plates assembled face to face areidentical to the tubes conjointly formed by the troughs of those plateswith the troughs of each of the plates facing them.

The above lamellar sedimentation system is based on the V-sedimentationprinciple, using one of the corners of the hexagonal section inclinedtube 4. The main advantage over the standard disposition in whichsedimentation takes place on one of the sides of the hexagon is thatthere is a much smaller area of friction between sludge and walls, whichreduces the friction forces that normally slow the downward movement ofthe sludge in the tube and therefore increases the rate of flow. Theconsequence of this is that, to evacuate the same volume of sludge, thelayer thickness is less, increasing the section available for the flowof water, therefore a lower downward speed, and therefore more effectiveseparation.

This is particularly clear from FIG. 4.

The tubular structure of the present blocks compared to plane plates ischaracterized by a greater hydraulic diameter, a lower Reynolds' numberand a shorter distance for the establishing of laminar flow (NB: theseconcepts are familiar to the person skilled in the art, the hydraulicdiameter being four times the hydraulic radius, for example, which isthe ratio of the wetted section (the section occupied by the flow) tothe wetted perimeter; these concepts are defined, for example in “Manueld'Hydraulique Générale, Armando Lencaster, Editions Eyrolles 1986, p.50. The consequence of this is a greater effective length than a planeplate sedimentation system, and thus a higher separation efficiency forexactly the same total length and separation.

The table below compares a block of the invention and a system withplane plates. Plane Invention plates Block width mm L 1020 1020 Tubewidth mm L1 60 1020 Number of — N = L/L1 17 1 parallel tubes Mean tubemm E 30 30 separation Wetted perimeter mm P1 166 2040 Tube inside areamm2 S1 = L*E 1800 30600 Total inside area mm2 S = S1*N 30600 30600Hydraulic diameter mm Dh = 4*S1/P1 43 60 Kinematic m/s2 n 1.15E−061.15E−06 viscosity Flow speed m/h V 10 10 Reynolds number — Re = V*Dh/n105 145 Transition length mm Lt = 131 250 0.02875*Dh*Re Total length mmLmax 1100 1100 Useful/total (Lmax − Lt)/Lmax 88% 77% length

The separation of the tubes, i.e. their hydraulic diameter, may bechosen as a function of the quantity of sludge to be extracted and therequired exit concentration. The separation is preferably greater forhighly charged effluents for which there is a high risk of clogging and,conversely, lower if it is required to increase the efficacy oftreatment.

Thus the hydraulic diameter is preferably selected from 30 mm to 100 mm,preferably from approximately 40 mm for lightly charged effluents toapproximately 80 mm for heavily charged effluents.

A number of remarks may be made regarding the blocks (certain of whichhave already been referred to above), remembering that these arepreferred, not essential, features.

The rectangular sedimentation plates are preferably provided withchannels or waffle patterns, for example formed by heat-forming; theterm “waffle pattern” might seem more appropriate than the term“corrugation” when the section of the troughs or the crests ispolygonal. The waffle patterns advantageously define an angle relativeto the base from 45° to 65°, preferably from 55° to 60°. The height ofthe plates is typically from 500 mm to 3000 mm, preferably from 900 mmto 1300 mm.

The thermoformed channels are preferably of trapezoidal shape to createclosed hexagonal shapes when the modules are constructed.

Each module consists of two parallel plates disposed in a mirror imagearrangement relative to their plane of contact.

Each block consists of a predetermined number of modules disposed inparallel (although there could alternatively be an odd number ofidentical plates, successively mounted head-to-tail). The width B ofeach block depends on the number of associated modules and takes accountof the width of the structure to be equipped, or even of the packagingmethod intended for transportation.

The blocks are of parallelepiped shape to facilitate installation instructures of all shapes and sizes; the last block of a row may beshortened to take account of the length of the structure to be equipped.

Each block may be equipped with hooks 5 (see FIG. 5), for example fourhooks, to facilitate handling (picking up and putting down) duringoriginal installation or for washing or replacement. Here these hooksare disposed along upper edges of the outside two plates of the block.Note here that the plates extend along the greatest dimension of theblock and that the width of the block (the depth in FIG. 5) isperpendicular to the plates.

The number of blocks to be disposed in parallel and their width aredefined as a function of the width of the sedimentation tank.

A plurality of blocks may be juxtaposed in the longitudinal direction,as a function of the total length of the tank and the length of eachblock.

FIG. 6 shows an arrangement of 12 modules, including 2×3 completemodules (with dimensions L×B), three modules of reduced breadth (lengthL1 but breadth B1), three modules of reduced length (length L1 andbreadth B) and a module with both dimensions reduced (length L1 andbreadth B1). Note that the blocks are contiguous and that as aconsequence of this the tubes of the blocks line up with each other (seeFIG. 7).

Each plate is advantageously cut laterally always at the same pointrelative to the trapezoidal profile to ensure perfect continuity betweentwo blocks disposed longitudinally. This ensures continuity of flow inthe sedimentation tubes belonging to two successive blocks, preventingthem from being clogged by deposited and non-evacuated sludge, which isindicated diagrammatically by the two arrows in FIG. 7 that cross theinterface between the two adjacent blocks.

As emerges from FIG. 8 in particular, in a rectangular sedimentationsystem, vertical flow spaces E may advantageously be provided betweenthe last block and the wall of the tank in order to ensure the use ofall the sedimentation tubes and thereby avoid the formation of depositsin the tubes. Note that this rectangular sedimentation system is simplyresting on supports 20.

In a rectangular sedimentation system like that of FIG. 8, horizontalplates (here represented by the same reference numbers as the supports20) are disposed at the top or bottom of each vertical corridor in orderto separate the untreated effluent from the effluent.

FIG. 9 represents a rectangular sedimentation system mounted in anactivated sludge channel, here suspended (for example by means of theFIG. 5 hooks 5) from a fixed structure 25 above the water level butwhich may instead rest on supports. A apron 40 is shown.

FIG. 10 represents a circular sedimentation system equipped with asuccession of blocks 10 mounted close to the wall, in front of theoutlet weir (not shown); as seen in FIG. 11, each block rests onsupports 15, for example.

FIG. 12 represents in section a sedimentation system including twoblocks on each side of a rectilinear offtake channel 30 (here in asuspended configuration).

1. Lamellar sedimentation module including two plates fixed together, atleast one of these plates having corrugations the crests and the troughswhereof are inclined to a first edge of this plate at a non-zero angleand delimit with the other plate inclined sedimentation tubes,characterized in that the two plates (2, 3) have the same corrugatedprofile and are fixed together in connecting areas defining a plane ofsymmetry (P) for the tubes (4) defined by these plates.
 2. Moduleaccording to claim 1, characterized in that the angle of inclination (α)is in the range 45°-65°.
 3. Module according to claim 2, characterizedin that the angle of inclination is in the range 55°-60°.
 4. Moduleaccording to claim 1, characterized in that the crests (2A, 3A) and thetroughs (2B, 3B) are of trapezoidal shape so that the sedimentationtubes are of hexagonal shape.
 5. Module according to claim 1,characterized in that the crests and the troughs have identicalprofiles.
 6. Module according to claim 1, characterized in that the twoplates are symmetrical to each other with respect to a plane of symmetryof the tubes.
 7. Module according to any one of claim 1, characterizedin that the plates are identical to each other.
 8. Module according toclaim 1, characterized in that the plates are of rectangular shape. 9.Module according to claim 1, characterized in that the tubes arerectilinear throughout their length.
 10. Lamellar sedimentation systemincluding at least one block (10) formed of a plurality of plates atleast one pair whereof constitute a module according to claim
 1. 11.System according to claim 10, characterized in that the block (10)includes at least two modules assembled so that these modules conjointlydelimit other tubes (4′), these modules being fixed together in areasdefining a plane of symmetry for these other tubes.
 12. System accordingto claim 11, characterized in that these other tubes (4′) have the samesection as the tubes (4) of each module.
 13. System according to claim10, characterized in that the modules are identical to each other. 14.System according to claim 10, characterized in that the block is ofrectangular parallelepiped shape, the plates being parallel to one ofthe faces of this block.
 15. System according to claim 14, characterizedin that the plates are perpendicular to the smallest dimension of theblock.
 16. System according to any one of claim 10, characterized inthat the block is disposed so that the plates are vertical and the firstedge is horizontal.
 17. System according to claim 16, characterized inthat the block is provided with attachment members by means whereof thisblock may be handled.
 18. System according to claim 17, characterized inthat the block is suspended from a fixed portion of the system. 19.System according to claim 10, characterized in that the block rests on afixed portion of the system.
 20. System according to claim 10,characterized in that it includes at least two juxtaposed identicalblocks so that the tubes of one of the blocks are in line with the tubesof the other block.
 21. System according to claim 10, characterized inthat the block is disposed near a tank wall to which the plates areperpendicular, leaving a space between this block and this wall. 22.System according to claim 10, characterized in that the tubes have ahydraulic diameter from 40 mm to 100 mm.
 23. System according to claim10, characterized in that the tubes have a length from 15 to 30 timestheir hydraulic diameter.